Where is XFCE configuration file located?

I was wondering where is XFCE configuration file regarding brightness, increasing or decreasing volume located. Function keys except for brightness keys doesn't work. There is also a indicator to show changes regarding brightness. I want to add features to mute/unmute audio device. I've binded function keys with alaxa mixer using keyboard shortcut but it doesn't seem satisfactory. No notation is shown, regarding any changes. So, it would be great if someone could guide me how to add these feature and where are these configuration file located.